Growing up in a large and broadly constituted early Albany family, he was a fur trader. As a young man, business led him to opportunities beyond the bounds of his father's Albany home. Consequently, he may not have married until he was in his thirties. His bride was a younger Maria Ketelhuyn - the mother of their nine children who, by 1709, were baptized at the Albany Dutch church.

As early as 1687, he was identified as an Albany merchant. In 1694, he was appointed constable in the third ward - where Barent Bradt had his house. Following his marriage, Johannes set up his own home on the corner of Market Street and Maiden Lane. He soon he became an Albany mainstay. In 1699, he joined with his neighbors in swearing allegiance to the king of England. Albany assessment rolls valued his third ward home comparably to those of other business people.

He was known as "Captain Bradt" probably by virtue of his militia connection. He was able to secure farmland beyond Albany - in the upper Hudson Valley and at Schaghticoke. Even before the coming of peace in 1713, he sought to develop those external holdings.

Unfortunately, those ambitions led to disaster as the frontier proved unsafe for him and his family. Although traditional sources range from less than credible to conflicting, there is some agreement that Johannes Barentse Bradt was killed by Indians following an incident at Schaghticoke on October 20, 1711. Several family members were killed and Bradt's son and wife were captured and taken to Canada.